Cant figure out how to stop it snowing... please help :(

Heya, new ish with flash and actionscript, learning at college and im enjoying it so much im rushing ahead and doing my own thing... thought i would be clever and create a snow effect, alas i cant get it to stop when i want to to, tried all sorts of stop; stopall; commands but its not happening...

Thanks either way for any help

Heres the code im using...

addEventListener (Event.ENTER_FRAME,snow);

function snow (event:Event):void {

    var scale:Number=Math.random()*.6;

    var _sf:Snowflake1=new Snowflake1();

    _sf.x=Math.random()*1024;

    _sf.scaleX=scale;

    _sf.scaleY=scale;

    var speed:Number=Math.random()*2;

    var RA:Array=new Array(-1,1);

    var lf:int=RA[Math.round(Math.random())];

    stage.addChild (_sf);

    _sf.addEventListener (Event.ENTER_FRAME,snowfall);

    function snowfall (event:Event):void {

        _sf.y+=speed;

        _sf.rotation+=Math.random()*20;

        _sf.x+=(Math.random()*2)*lf;

    }

}

Thanks again either way